Regarding the "Witten DMT process" (Katzschmann process), reference may be made to German Patent 10 41 945, German Patent 12 99 627, DE-A-20 14 012, DE-C3-22 44 662, DE-C3-24 27 875, DE-C2-29 16 197, DE-C2-30 11 858, DE-C2-30 37 045, DE-C2-30 44 617, EP-B1-0 053 241, DE-C1-31 51 383, EP-B1-0 156 133, EP-B1-0 157 122, DE-C1-34 40 650 and WO 90/909367 and Hydrocarbon Processing, November 1983, page 91. Where reference is made in the present description to the total process, these publications are referred to.
The off gas from the oxidation by the Witten DMT process is usually cooled in several stages, the relatively high-boiling and medium-boiling components substantially condensing stepwise. After scrubbing with cold water, the off gas stream is substantially freed from residual organic constituents in an activated carbon adsorption (Ullmann, 4th Edition 1982, Volume 22, page 529 et seq.; DE-C1-34 40 650 and DE-A1-24 61 092).
A similar waste gas purification with cooling and subsequent scrubbing with water is known for the oxidation waste gases in the so-called AMOCO process (Ullmann, 4th Edition 1982, Volume 22, page 519 et seq.).
In order to utilize the stored mechanical energy, it is usual to use the off gases, which are under a pressure of 5 to 15 bar, in an expansion turbine for driving a compressor for inlet air.
This off gas purification has the disadvantage that the energies contained in the off gas can be utilized only to a limited extent. Finally, it is not possible to remove the CO present in the off gas by means of desorption using activated carbon. Another disadvantage is that the adsorption stage (activated carbon plant) can only be operated discontinuously and that working up of the activated carbon desorbate is expensive.
GB-A-2 097 476 (=DE-A1-32 15 437) discloses a process for utilizing the mechanical energy of a residue gas, in which the residue gas is used for cooling a gas turbine with subsequent mixing the residue gas with the combustion off gas. Combustion of the residue gas is neither intended nor possible in this process.
EP-A- 0 222 158 discloses a process for removing organic impurities from a gas. Preferably, the impurities are condensed in a first stage of purification and the remaining impurities are burnt in a second purification stage. The energy gained from this second stage of purification for inst. can be utilised for the generation of current. EP-A 0 222 158, however, does not make reference to the purification of an off-gas from a reaction process operated under pressure.
DE-A- 27 59 208 discloses the utilization of solvent vapours in exhaust air for operating combustion aggregates. At this the off-gas loaded with organic solvents can be burnt. The units for thermal burning of solvents can be utilised for heat generation. Furthermore it is possible to perform a conversion into mechanical energy. DE-A- 27 59 208 also does not disclose the purification of an off-gas from a reaction process operated under pressure.